The invention relates to the field of client/server (also known as xe2x80x9cdistributedxe2x80x9d) computing, where one computing device (xe2x80x9cthe clientxe2x80x9d) requests another computing device (xe2x80x9cthe serverxe2x80x9d) to perform part of the client""s work.
Client/server computing has become more and more important over the past few years in the information technology world. This type of distributed computing allows one machine to delegate some of its work to another machine that might be, for example, better suited to perform that work. For example, the server could be a high-powered computer running a database program managing the storage of a vast amount of data, while the client is simply a desktop personal computer (PC) which requests information from the database to use in one of its local programs.
The benefits of client/server computing have been even further enhanced by the use of a well-known computer programming technology called object-oriented programming (OOP), which allows the client and server to be located on different (heterogeneous) xe2x80x9cplatformsxe2x80x9d. A platform is a combination of the specific hardware/software/operating system/communication protocol which a machine uses to do its work. OOP allows the client application program and server application program to operate on their own platforms without worrying how the client application""s work requests will be communicated and accepted by the server application. Likewise, the server application does not have to worry about how the OOP system will receive, translate and send the server application""s processing results back to the requesting client application.
Details of how OOP techniques have been integrated with heterogeneous client/server systems are explained in U.S. Pat. No. 5,440,744 and European Patent Published Application No. EP 0 677,943 A2. These latter two publications are hereby incorporated by reference. However, an example, of the basic architecture will be given below for contextual understanding of the invention""s environment.
As shown in FIG. 1, the client computer 10 (which could, for example, be a personal computer having the IBM OS/2 operating system installed thereon) has an application program 40 running on its operating system (xe2x80x9cIBMxe2x80x9d and xe2x80x9cOS/2xe2x80x9d, are trademarks of the International Business Machines corporation). The application program 40 will periodically require work to be performed on the server computer 20 and/or data to be returned from the server 20 for subsequent use by the application program 40. The server computer 20 can be, for example, a high-powered mainframe computer running on IBM""s MVS operating system (xe2x80x9cMVSxe2x80x9d is also a trademark of the IBM corp.). For the purposes of the present invention it is irrelevant whether the requests for communications services to be carried out by the server are instigated by user interaction with the first application program 40, or whether the application program 40 operates independently of user interaction and makes the requests automatically during the running of the program.
When the client computer 10 wishes to make a request for the server computer 20""s services, the first application program 40 informs the first logic unit 50 of the service required. It may for example do this by sending the first logic unit the name of a remote procedure along with a list of input and output parameters. The first logic unit 50 then handles the task of establishing the necessary communications with the second computer 20 with reference to definitions of the available communications services stored in the storage device 60. All the possible services are defined as a cohesive framework of object classes 70, these classes being derived from a single object class. Defining the services in this way gives rise to a great number of advantages in terms of performance and reusability.
To establish the necessary communication with the server 20, the first logic unit 50 determines which object class in the framework needs to be used, and then creates an instance of that object at the server, a message being sent to that object so as to cause that object to invoke one of its methods. This gives rise to the establishment of the connection with the server computer 20 via the connection unit 80, and the subsequent sending of a request to the second logic unit 90.
The second logic unit 90 then passes the request on to the second application program 100 (hereafter called the service application) running on the server computer 20 so that the service application 100 can perform the specific task required by that request, such as running a data retrieval procedure. Once this task has been completed the service application may need to send results back to the first computer 10. The server application 100 interacts with the second logic unit 90 during the performance of the requested tasks and when results are to be sent back to the first computer 10. The second logic unit 90 establishes instances of objects, and invokes appropriate methods of those objects, as and when required by the server application 100, the object instances being created from the cohesive framework of object classes stored in the storage device 110.
Using the above technique, the client application program 40 is not exposed to the communications architecture. Further the service application 100 is invoked through the standard mechanism for its environment; it does not know that it is being invoked remotely.
The Object Management Group (OMG) is an international consortium of organizations involved in various aspects of client/server computing on heterogeneous platforms with distributed objects as is shown in FIG. 1. The OMG has set forth published standards by which client computers (e.g. 10) communicate (in OOP form) with server machines (e.g. 20). As part of these standards, an Object Request Broker (ORB) has been defined, which provides the object-oriented bridge between the client and the server machines. The ORB decouples the client and server applications from the object oriented implementation details, performing at least part of the work of the first and second logic unit 50 and 90 as well as the connection unit 80. So, there is usually an ORB software component running on both the client and the server computers so that the client and server can communicate with each other in order to make use of each other""s local objects.
It is often desirable to provide so-called xe2x80x9cthinxe2x80x9d(or light-weight) clients which contain a minimum amount of software functionality so that the client machine can be made easily portable (e.g., a set-top box, personal digital assistant (PDA), laptop computer, or computerized cellular telephone with display screen). However, the thinner the client the less functionality the client is capable of supporting. Thus, it has been difficult to use xe2x80x9cthinxe2x80x9d clients in situations where the client must be available to serve requests which could involve a wide variety of functionality.
According to one aspect, the present invention provides a data processing apparatus in communication with a network for allowing the apparatus to communicate with a second data processing apparatus via the network, the data processing apparatus comprising: a receiving unit for receiving a request on a target object; an activating unit for activating the target object if the target object is inactive; and a dispatching unit for dispatching the request to the target object for execution thereby; wherein the activating unit determines whether software components which it needs to activate the target object are stored locally and if it determines that the software components are not stored locally the activating unit downloads such software components over the network from the second data processing apparatus; and wherein the activating unit selects candidate software components from the locally stored software components based on predetermined criteria and deletes the candidate software components from local storage.
According to a second aspect, the present invention provides a method of carrying out the functionality of the first aspect of the invention.
According to a third aspect, the present invention provides a computer program product, stored on a computer readable storage medium, for, when run on a computer, instructing the computer to carry out the functionality of the first aspect of the invention.
Thus, with the present invention, a client machine""s working set of software code is allowed to dynamically xe2x80x9cgrowxe2x80x9d and xe2x80x9cshrinkxe2x80x9d depending on demand. This makes a thin client much better able to participate in a distributed computing environment (such as an ORB setting) where the client can be called upon to perform a wide variety of tasks yet still remain xe2x80x9cthinxe2x80x9d (or lightweight in terms of the amount of active software code in the client""s working set). Specifically, if the client is called upon to do a particular task at one point in time, the client makes sure that it has the appropriate software components in its working set by, if necessary, downloading such software components into its working set from a server machine over the network (if the software components are already in the working set, then there is no need for such downloading). At a later point in time, for example, if such downloaded components have not been used for awhile, they can be deleted from the working set to keep the client""s working set small. The invention thus enables a thin client to participate fully in a distributed processing environment (such as an ORB setting).